This invention generally relates to a method of manufacturing a solid state color imaging device which detects incident light so as to produce a color image signal, and more particularly relates to a method of manufacturing the solid state color imaging device incorporating a color filter on the solid state imaging device.
A color television camera consists of one or two solid state imaging devices such as a charge-coupled device, bueket brigade device and metal oxide semiconductor. The solid state imaging device requires a mosaic or stripe-shape color filter for color separation. In these conventional color imaging devices, the color filter formed on the surface of the transparent substrate, such as glass, is disposed on the solid state imaging device while the color filter is precisely aligned so as to fit each imaging element provided on the solid state imaging device. Such alignment is difficult, increases manufacturing cost and reduces yield rate. Therefore in recent years it has been proposed that the color filter be directly installed on the solid state imaging device by the so-called on-chip method.
There are two typical methods for directly forming the color filter on the solid state imaging device.
One manufacturing method is illustrated in FIGS. 1 (a) to (c).
Photosensitive liquid is applied over the surface of a solid state imaging device 1 by a roll coat method, dipping method or spinner method. The photosensitive liquid contains dyeable resin such as polyvinyl alcohol, glue, gelatin and casein and is doped by ammonium bichromate to impart photosensitivity. The applied photosensitive liquid is dried. The photosensitive layer to be dyed with a first color is selectively exposed to light to be cured by using a photo mask. Then the photosensitive layer is developed and removed from the solid state imaging device 1 except for the photochemically cured portion which is to be dyed and which is called a dye base layer 2. The dye base layer 2 forms a predetermined filter pattern. The dye base layer 2 is colored by dye having a predetermined spectral characteristics. A clear anti-dyeing material is applied over the solid state imaging device to form an anti-dyeing layer 3 which is not dyed by any dye (see FIG. 1 (a)).
As shown in FIG. 1 (b) and in a manner the as same as above mentioned, the photosensitive liquid is applied over the anti-dyeing layer 3 and is dried to form another photosensitive layer. The photosensitive layer is selectively exposed to light through a photo mask (not shown). The photosensitive layer is developed to form a second dye base layer 4. The second dye base layer 4 is colored by another dye having predetermined spectral characteristics. The anti-dyeing material is then applied over the second dye base layer 4 to form a clear anti-dyeing layer 5.
As shown in FIG. 1 (c), the photosensitive liquid is applied over the anti-dyeing layer 5. The photosensitive liquid is dried to form the photosensitive layer. The photosensitive layer is selectively exposed to light through a photo mask and is developed to form a third dye base layer 6. The third dye base layer 6 is colored by a different dye having predetermined spectral characteristics. Finally a top coat layer 7 is provided over the entire colored layer to form the color filter.
However such a conventional method of manufacturing the color filter has the following drawbacks.
1. The first dye base layer 2 and the second and third dye base layers 4 and 6 are disposed on different surfaces. The first dye base layer 2 is provided directly on the surface of the solid state imaging device. In turn the second and third dye base layers are formed on the anti-dyeing layers 3 and 5 respectively. The adhesive strength of the photosensitive layer differs for different substances. For instance some photosensitive layers strongly adhere to the surface of the solid state imaging device (generally made of SiO.sub.2 film) while the same photosensitive layers are easily removed from the anti-dyeing layer.
2. The anti-dyeing layers 3 and 5 cause positional differences among the first, second and third dye base layers in the film thickness direction. Such positional differences reduce the resolution of the color filter pattern. Therefore the pattern of the second and third dye base layers is not sharp.
3. Uneven surface of the solid state imaging device prevents the uniform application of the photosensitive liquid so that the thickness of the dye base layer is not kept constant. Namely, the color density of the color filter is not constant. For to the same reason, it is difficult to form an accurate dyed region of mosaic or stripe-shape.
4. The light exposure process is required three times. The process is complicated and requires many steps so that cost reduction is difficult to achieve.
The second conventional method of manufacturing the solid state color imaging device is illustrated in FIGS. 2 (a) to (d). As shown in FIG. 2 (a), a dyeable resin is applied over the surface of the solid state imaging device 1 by a roll coat method, dipping method or spinner method to form a dye base layer 2.
Next as shown in FIG. 2 (b), a photoresist layer is formed on the dye base layer 2.
The photo-resist layer is photo-etched to form a first dyeing mask 8 which has openings in a predetermined pattern. The dye base layer 2 is selectively dyed through the mask openings by a first dye having predetermined spectral characteristics to form a first color filter layer 21.
Next as shown in FIG. 2 (c), a second dyeing mask 8' having openings is formed by the light exposure method. The dye base layer 2 is selectively dyed through the second mask openings by a second dye having predetermined spectral characteristics to form a second color filter layer 22. The process is then repeated a third time and a third color filter layer 23 is formed to constitute the color filter as shown in FIG. 2 (d).
This manufacturing method, in comparison with the first conventional manufacturing method, directly forms the dye base layer on the solid state imaging device and thus eliminates the positional difference among different color filter layers. Therefore the drawbacks 1 and 2 of the first conventional manufacturing method may be removed. However, the drawbacks 3 and 4 of the first conventional manufacturing method also exist in the second conventional method. Further, according to the second conventional method, the first, second and third color filter layers 21, 22 and 23 are formed closely adjacent one other so that the dye tends to diffuse into the adjacent regions. Therefore the different colors become mixed together.